deposit.
The pegmatites form sheetlike or lenticular masses, and the emerald
vein proved to be one of the latter. It had a warped east-west strike,
and ran close, to, if it did not join, a bulge or boss of pegmatitic
granite encountered in the tunnel in the oast end of the cut. The vein
ranged from a seam up to 6 feet in thickness, with a length of about 40
feet and a depth of about 20 feet. It is possible that further work
might expose other pegmatite lenses deeper and farther west opening out
in the continuation of the seam left where the original vein pinched
out. Other veins almost identical in appearance with the original
emerald vein were found near by, and some of these are being prospected
for emeralds.
The
pegmatite of the emerald vein was medium to coarse grained, and was
composed of quartz and feldspar, part of which was albite, wdth some
black tourmaline and a little beryl. A few small irregular microlitic
cavities were found, and in these the minerals assumed partly developed
crystal form. In some of the pegmatites bluish-green apatite occurs,
especially in the mass of pegmatitic granite. A few stout crystals of
albite and of smoky and colorless quartz have been found in the
pegmatite veins. Some of the quartz contains numerous light-colored
needle-like inclusions of actinolite. The pegmatite is partly
decomposed, so that some of it is ready for washing on sieves, but
some is mined in large blocks, which have to be broken separately and
examined for emeralds. So far true emeralds have been found hi only one
vein, but the similarity in the association of minerals and of
inclosing rocks in the other pegmatites is considered promising.
In
the opening 90 feet south of east of the cotton-boll pit a pegmatite
vein was encountered carrying small, clear, nearly colorless beryl
crystals and cylindrical rutile crystals, some of which show brilliant
red streaks. The beryl crystals yield very brilliant stones when cut.
The part of the vein opened appears to he south of the hornblende
hypersthenite area, and the vein will be prospected along its northerly
strike to that rock. In the trench 200 feet east of the cotton-boll pit
beryl crystals were found in pegmatite at a depth of 12 feet. These
crystals were rough in form and of poor quality, with a greenish color.
One piece contains some patches of true aquamarine. These beryl
crystals ranged from small size up to 2 inches in diameter.
The
emerald crystals are being cut preparatory to the market. Several fine
specimens are still intact. A fire at the emerald mine in April, 1913,
destroyed a quantity of the rough matrix specimens and associated
minerals, so that now only a few of such specimens are available.
AUSTRALIA.
A discovery of green beryl and emerald has been reported near Poonah, on the Murchison gold field1 in
western Australia. The occurrence was brought to light through the
efforts of H. P. Woodward, assistant government geologist, who
assisted in tracing back specimens to then- source. The
crystals have been found scattered over the surface in dusty soil
formed by the decomposition of schist country rock. No work had been
done at the time of Mr. Woodward's 'visit. The formation has been
traced nearly 2 miles in a
1 Mm. Jour., London, March 29,1913.
